If you have not listened to Meredith Monk before, I recommend it. Her style of music is abstract and eclectic, and her voice control brings a large range of sounds and effects to the medium.
I dont think I can make it out in this recording, but she is able to control her singing in the harmonic high notes made popular by the Tuvan throat singers. I believe this is quite difficult because the harmonics are created by beating two tones against each other, so small changes make large effects.